This invention relates to systems and methods for control of electromechanical actuators and, in particular, to a system and method for controlling the impact or landing of an armature of the actuator against the pole face of an electromagnet of the armature.
Electromechanical actuators are used in a variety of locations within conventional vehicle engines to control various engine operations. For example, fuel injectors and camless engine valves often include such actuators. A typical two-position electromagnetic actuator includes an armature disposed between a pair of opposed electromagnets. Springs on either side of the armature locate the armature in a neutral position between the electromagnets when the electromagnets are not energized.
To initiate movement of the actuator between the electromagnets, current in the holding electromagnet is switched off. The force of the compressed spring causes the armature to move toward the aforementioned neutral position. At a certain point, the other electromagnet is energized to attract the armature. The magnetic force of attraction between the armature and electromagnet is inversely proportional to the square of the distance between the armature and the electromagnet. Accordingly, the magnetic attraction force increases faster than the linearly increasing force of the opposing spring. As a result, the armature may attain an undesirably high speed as it approaches and lands on the pole face of the electromagnet. This results in undue wear on the mechanical components of the actuator as well as undesirable acoustic noise.
A variety of methods and systems have been developed to control or otherwise limit the speed of the armature as it approaches the pole face of the electromagnet. Conventional methods and systems, however, are relatively complex-requiring extensive measurements or complex calculations to control the armature. Further, conventional systems and methods are often unable to account for unknown disturbances acting on the armature such as gas pressures and eddy currents in the release electromagnet.
The inventors herein have recognized a need for a system and method for controlling movement of an armature towards a pole face of an electromagnet in an electromagnetic actuator that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a system and a method for controlling movement of an armature towards a pole face of an electromagnet in an electromagnetic actuator in which the armature moves toward the pole face against a force of a restoring spring when a coil of the electromagnet is charged with a current. A method in accordance with the present invention includes the step of providing the current to the coil of the electromagnet. The method also includes the step of determining a neutral position for a virtual spring after the armature reaches a predetermined position. The virtual spring has a virtual spring force corresponding to a combination of a magnetic force generated by the electromagnet responsive to the current and a restoring spring force generated by the restoring spring. The method finally includes the step of controlling the current responsive to the neutral position of the virtual spring.
A system in accordance with the present invention includes means for providing current to the coil of the electromagnet and an electronic control unit. The electronic control unit is configured to determine a neutral position for the virtual spring after the armature reaches a predetermined position and to control the current responsive to the neutral position of the virtual spring.
The present invention represents an improvement as compared to conventional systems and methods for controlling movement of an armature towards a pole face of an electromagnet against a restoring spring. In particular, the inventive system and method accurately and efficiently control the velocity of the armature as it approaches the pole face of the electromagnet thereby reducing the impact velocity of the armature. As a result, wear on the mechanical components of the actuator is minimized and acoustic noise significantly reduced. Further, the inventive method and system are robust relative to unknown disturbance forces such as viscous damping that act on the armature as long as the disturbance forces are dissipating. Finally, the inventive method and system are not as complex as conventional methods and systems.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.